Optically baffled throated nozzle



Dec. 19, 1967 x x 3 :1 1 JLL 2 gm UJI 1- 0.5 1 :1 o u z o a: 2 m

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WITNESSES H WU mm mam-111:1;

OPTICALLY BAFFLED THROATED NOZZLE Filed June 8, 1964 PRIOR ART I THROAT NOZZLE WALL AXIAL POSITION Fig.I

OPTICAL BAFFLE NOZZLE WALL AXIAL POSITION Fig.

INVENTOR Joel B. Hummer ATTORNEY United States Patent 3 358 503 OPTICALLY BAFFIjED THROATED NOZZLE Joel B. Hammer, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed June 8, 1964, Ser. No. 373,148 6 Claims. (Cl. 73147) This invention relates to improvements in nozzles for use in arc heaters and plasma jet generators, and more particularly to an improved nozzle having an optical bafile therein for reducing the heat load in the vicinity of the nozzle throat.

The handling of high total temperature gases in nozzles is accompanied by problems which have not been satisfactorily met in prior art apparatus. Wind tunnel testing of models under reentry conditions is one example; it involves a convergent-divergent nozzle handling air up to 20,000 R. total temperature. In such a nozzle an extremely high heat load must be handled in the vicinity of the nozzle throat. This high heat load is primarily the result of the radiant flux and the convective flux each being large and approximately the same order of magnitude. Fluid cooling of the nozzle area and fins and other devices for increasing the heat removal from the nozzle have not provided a satisfactory solution to the problem, since most cooling systems have a burn-out heat flux which limits the heat flux from the gas in the nozzle area.

In my invention the problem of high heat load in the vicinity of the nozzle throat is alleviated by significantly reducing the radiant flux in the region where the convective flux is high. To this end my invention includes, but is not limited to, an optical baflle disposed in the nozzle upstream of the throat and at a position along the longitudinal axis of the nozzle which would correspond approximately to the position of maximum heat flux. My invention results in a substantially 50% reduction in the total heat fiux, that is, the heat flux due to both radiation and convection, with the result that are heater or plasma jet generator apparatus embodying my invention can utilize gases at temperatures approximately twice those which could be reached without the use of my invention.

Accordingly, a primary object of my invention is to provide a new and improved nozzle offering advantages in heat load reduction over any nozzle now existing in the art.

Another object is to provide a new and improved nozzle having an optical bafile therein for reducing the heat radiation falling upon the throat region of the nozzle.

A further object is to provide a new and improved nozzle in which the peak heat flux is substantially reduced.

An additional object is to provide a new and improved nozzle having an optical bafile which will permit gases to be heated to increased temperatures without burning out the nozzle.

These and other objects of the invention will appear more clearly hereinafter after a study of the following specification, when taken in connection with the accompanying drawings, in which:

FIGURE 1 is a graph illustrating heat flux as a function of distance along the longitudinal axis of the nozzle, in a typical nozzle constructed according to the prior art; and

FIG. 2 is a combined cross-sectional nozzle view and graph showing the optical bafile of my invention and the heat flux characteristic of a nozzle having the optical bafile.

In FIG. 1, to which particular reference is made, the nozzle is shown diagrammatically at 10, having a throat 11 and an exhaust portion 12. As drawn, the nozzle generally designated is placed in a system of rectilinear coordinates in which the distance along the axis of the 3,358,503 Patented Dec. 19, 1967 nozzle, or the axial position, is the abscissa, and the ordinate is a scale of the ratio of local heat flux to burn out heat flux. Local heat flux means the flux at any position measured along the longitudinal axis of the nozzle. Variations in flux along the longitudinal axis of the nozzle are illustrated by the curve 15, the ordinate scale being shown at 16, and the abscissa at 17. It will be noted that the flux ratio at an axial position slightly in advance of the narrowest portion of the nozzle throat reaches a peak value which is almost unity; unity would represent a value corresponding to the burnout heat flux which would result in the destruction of the nozzle material. This high peak heat flux just upstream of the nozzle throat is due to strong contribution by both radiation and convection. It may be noted that at a position just downstream of the throat, where the convective flux is quite high but the location or axial position is out of view of the hot reservoir of gas in the arc heater or plasma generator, the heat flux becomes much lower than the peak value, as indicated by curve 15.

For a more detailed understanding of the distribution of the heat flux in the nozzle reference may be had to an article by W. E. Welsh, Jr., and A. B. Witte, entitled A Comparison of Analytical and Experimental Local Heat Fluxes in Liquid-Propellant Rocket Thrust Chambers," Journal of Heat Transfer, February 1962.

Particular reference is made now to FIG. 2 which shows the nozzle of my invention with the optical bafiie therein. As in FIG. 1, the nozzle is shown diagrammatically and generally designated 20, having a throat 21 and an exhaust portion 22 with axial position along the longitudinal axis of the nozzle being plotted along the abscissa of a pair of rectilinear coordinates, the ordinate scale indicating the ratio of local heat flux to burnout heat flux, the local heat flux being indicated by the curve 25, the ordinate scale being 26, the abscissa being 27, and the optical bafile being shown at 28. Any convenient means, not shown, may be employed for securely mounting the bafiie in position in the nozzle, such for example, as a stem-like support extending from the upstream end along the axis of the nozzle. The optical bafile may be composed of any suitable highly heat resistive material such, for example, as a ceramic such for example a compound of zirconium oxides, or a suitably cooled metallic material, for example. The two graphs of FIGS. 1 and 2 are plots for a nozzle having the same total temperature gas. It is seen that the total heat flux with the bafile does not reach a peak value equal to even one-half of the burnout heat flux. This is due to the fact that heat of radiation which would otherwise reach the throat area 21 is substantially totally cut off by the optical bafiie 28. The elimination of the peak of FIG. 1 means that the entire heat flux level may be increased (high total temperature gas). Since the radiation contribution near the throat is virtually eliminated by the bafile, the flux peak is essentially determined by the convective flux, which in turn, to a first approximation is proportional to the temperature of the gas. Thus, the optically bafiled throated nozzle of my invention can be operated with a gas having approximately twice the total temperature.

Other shapes and sizes of the optical bafile may, of course, be employed as desired, in accordance with the shape and dimensions of the nozzle. An eificient shape for the bafile is the frusto-conical configuration shown in FIG. 2, with the surface facing the arc chamber being convex.

Other means than those suggested may be employed for mounting the optical bafile securely in position in the nozzle.

Whereas I have shown and described my invention with respect to an embodiment thereof which gives satisfactory 9 -.9 results, it should be understood that changes may be made and equivalents substituted without departing from the spirit and scope of the invention.

I claim as my invention:

1. Nozzle apparatus for use in arc heaters and plasma generators having a chamber containing incandescent gas comprising, in combination, an exhaust nozzle for the chamber having a throat portion of restricted diameter at a predetermined position along the longitudinal axis of the nozzle, and an optical bafile composed of a highly heat resistive material mounted in the nozzle upstream of the throat portion, the optical baflle being constructed and arranged to prevent substantially any radiation from the incandescent gases in the chamber from falling on the inner wall of the nozzle over a predetermined portion thereof including the throat portion to thereby reduce the heat flux at the throat portion.

2. Nozzle apparatus according to claim 1 in which the optical bafile is additionally characterized as being generally frusto-conical in shape with the surface of smaller diameter facing the throat portion of the nozzle.

3. Nozzle apparatus for use in an arc heater or plasma generator wherein gases are heated to very high temperatures comprising, in combination, nozzle means composed of a material having a predetermined burnout temperature and having a throat of reduced diameter at a predetermined position along the longitudinal axis of the nozzle means, and means disposed in the nozzle means between the throat and the incandescent gases for preventing radiation from the gases from falling upon the wall of the nozzle means in the throat area thereof and over a portion of the Wall upstream of the throat to thereby prevent the formation of a heat flux peak approaching burnout temperature.

4. Nozzle apparatus according to claim 3 wherein the means for preventing radiation from the gases from falling on the throat of the nozzle means consists of a bafile member composed of a highly heat resistant material having predetermined dimensions.

5. Nozzle apparatus for use in gas heating apparatus wherein gases are heated to incandescence comprising, in combination, nozzle means having a throat of restricted diameter at a predetermined axial position along the length of the nozzle means, and optical batiie means composed of a highly heat resistive material and located in the nozzle means upstream of the throat, the optical baftie means preventing substantial direct radiation from said incandescent gases from falling on the wall of the nozzle means in the throat area thereof and for a predetermined distance upstream of the throat area, the optical baflle means causing the total heat flux in the nozzle throat area to correspond substantially to the heat flux resulting from the heat of convection and preventing the formation of a marked heat flux peak at any point along the length of the nozzle means.

6. Nozzle apparatus for use in gas heating equipment where gases are heated to incandescence in a chamber comprising, in combination, nozzle means for the chamber having a throat of reduced diameter at a predetermined axial position along the length of the nozzle means, the heat of convection and heat of radiation from the incandescent gases normally causing a heat flux peak in the nozzle means at a position on the upstream side of the throat area, and baffie means composed of a highly heat resistive material mounted in the nozzle means on the upstream side of the throat and preventing direct radiation from reaching the nozzle wall in the throat area thereby reducing the total heat flux in the throat area to substantially one-half of its normal value.

References Cited UNITED STATES PATENTS 3,066,528 12/1962 Giannini et al. 73147 3,133,410 5/1964 Gessner -35.6

DAVID SCHONBERG, Primary Examiner. 

1. NOZZLE APPARATUS FOR USE IN ARC HEATERS AND PLASMA GENERATORS HAVING A CHAMBER CONTAINING INCANDESCENT GAS COMPRISING, IN COMBINATION, AN EXHAUST NOZZLE FOR THE CHAMBER HAVING A THROAT PORTION OF RESTRICTED DIAMETER AT A PREDETERMINED POSITION ALONG THE LONGITUDINAL AXIS OF THE NOZZLE, AND AN OPTICAL BAFFLE COMPOSED OF A HIGHLY HEAT RESISTIVE MATERIAL MOUNTED IN THE NOZZLE UPSTREAM OF THE THROAT PORTION, THE OPTICAL BAFFLE BEING CONSTRUCTED AND ARRANGED TO PREVENT SUBSTANTIALLY ANY RADIATION FROM THE INCANDESCENT GASES IN THE CHAMBER FROM FALLING ON THE INNER WALL OF THE NOZZLE OVER A PREDETERMINED PORTION THEREOF INCLUDING THE THROAT PORTION TO THEREBY REDUCE TO HEAT FLUX AT THE THROAT PORTION. 